1. He is taking the diaper off because he is uncomfortable. BIG SIGNAL that is time to potty train and a really good reason not to force him to stay in it. How well do you sleep if you are uncomfortable anyway?
2. Ask him to sit on the potty about 15 minutes before naptime. While he sits read stories, play clapping games, sing songs etc so that it is fun to see there. He may not poop, but he might and he'll most likely at least pee if he is relaxed enough. Don't sit so long waiting that he becomes uncomfortable, but at least give him the chance to "get it out" before nap so that he isn't laying in a mess during nap. This may help temendously with potty training as well anyway. Leave enough time to still do your regular nap time routine after the potty part.
3. Put him in pull ups (during naps only, regular pants the rest of the time so he can still feel the wetness) and let him get up during nap to use the potty if he "feels the need". Let him know he should come get you. That way you can help clean him up without a huge mess if he is waking up dirty. I know it means an interruption to nap and that sucks, but if he gets the hang of potty training relatively quickly this will only go on for a month or two.
4. You may be concerned he will begin to use this as an excuse not to take a nap and the reality is that MIGHT happen, if it does you can cross that bridge when it comes. Once he is fully potty trained you can say things like, "you should only need to get up to go potty once". . .
5. Expect him to sleep later and alter his sleep schedule if needed to help avoid bowel movements during sleep.

It is a tough transition that affects sleep, your entire schedule really and means messes and accidents for awhile, but think about this: once you bite the bullet and make the transition, you won't be buying diapers anymore, (although you'll still be lugging around a big bag of kid stuff), having to find places to stop and change the diaper and you can plan ahead by asking him to go when you ARE near a potty.

For the actual potty training - there are LOTS of ways to go about doing it. You are even lucky enough to have him telling you he wants to potty train when it is summer and he can safely and comfortably play naked at times (immediate understand of the "prefeeling" before peeing and the other one, because he will see it happen) A quick search will give you lots of options for techniques and I believe there are a number of questions about potty training right here on stack exchange.

I personally think the best way is to get them comfortable with the toilet (its sounds, sitting on one, washing hands after . . .) by spending time in the bathroom together singing songs, play hand clapping games, I used to sing to my 2's class, "tinkle tinkle in the potty, get that stuff out of your body, it is so much better for you, to use the potty for your pee pee and your poo, tinkle tinkle in the potty. . . It always got a laugh. I would also suggest you spend this time in the bathroom reading books about going potty. There is a book with Elmo with buttons that talks about buying "big boy pants" and the whole process where Elmo teaches one of his dolls how to go potty that was great. There is also "no more diapers for ducky" and a set of books that is something like "the potty book for boys" and "the potty book for girls" that are all really good (plus numerous others)

1. He is taking the diaper off because he is uncomfortable. BIG SIGNAL that is time to potty train and a really good reason not to force him to stay in it. How well do you sleep if you are uncomfortable anyway?
2. Ask him to sit on the potty about 15 minutes before naptime. While he sits, read stories, play clapping games, sing songs etc so that it is fun to be there. He may not poop, but he might and he'll most likely at least pee if he is relaxed enough. Don't sit so long waiting that he becomes uncomfortable, but at least give him the chance to "get it out" before nap so that he isn't laying in a mess during nap. This may help temendously with potty training as well anyway. Leave enough time to still do your regular nap time routine after the potty part.
3. Put him in pull ups (during naps only, regular pants the rest of the time so he can still feel the wetness) and let him get up during nap to use the potty if he "feels the need". Let him know he should come get you. That way you can help clean him up without a huge mess if he is waking up dirty. I know it means an interruption to nap and that sucks, but if he gets the hang of potty training relatively quickly this will only go on for a month or two.
4. You may be concerned he will begin to use this as an excuse not to take a nap and the reality is that MIGHT happen, if it does you can cross that bridge when it comes. Even if you waited, this issue will arise eventually anyway. In a classroom of 20 "2's" we always had 1 or 2 kids for whom this became an issue (true in the threes as well). It is just one of the realities of toddlerhood some parents must find a way to deal with. Once he is fully potty trained you can say things like, "you should only need to get up to go potty once". . .
5. Expect him to sleep later and alter his sleep schedule if needed to help avoid bowel movements during sleep.

It is a tough transition that affects sleep, your entire schedule really and means messes and accidents for awhile, but think about this: once you bite the bullet and make the transition, you won't be buying diapers anymore, (although you'll still be lugging around a big bag of kid stuff), having to find places to stop and change the diaper will be in the past and although you will still need to find potties, you can plan ahead by asking him to go when you ARE near a potty. This will reduce accidents, rushing around in a panic, and is an introduction to teaching him about "planning ahead" for other things in life too.

For the actual potty training - there are LOTS of ways to go about doing it. You are even lucky enough to have him telling you he wants to potty train when it is summer and he can safely and comfortably play naked at times (immediate understanding of the "prefeeling" before peeing and the other one, because he will see it happen) A quick search will give you lots of options for techniques and I believe there are a number of questions about potty training right here on stack exchange.

I personally think the best way is to get them comfortable with the toilet (its sounds, sitting on one, washing hands after . . .) by spending time in the bathroom together singing songs, play hand clapping games, I used to sing to my 2's class, "tinkle tinkle in the potty, get that stuff out of your body, it is so much better for you, to use the potty for your pee pee and your poo, tinkle tinkle in the potty. . . It always got a laugh.

I would also suggest you spend this time in the bathroom (and out) reading books about going potty. There is a book with Elmo with buttons (that make noises like the toilet flushing and water running in the sink) that talks about buying "big boy pants" and the whole process as well as an episode that can be purchased all about potty training where Elmo helps (I think it's baby bear's little sister if I remember correctly) with her potty training and we meet Elmo's dad etc. There is even a song called "accidents happen". There is also "no more diapers for ducky" (another book) and a set of books that is something like "the potty book for boys" and "the potty book for girls" that are all really good (plus numerous others)