I reckon it's quite warm right now, and that's how males of several mammal species
react to it. If it's warm at your location right now - normal. That's the whole point of not having testicals internal. No worry. Other than that he might become temporarily heat sterile, but that doesn't seem to be a worry of yours.
Give him something cool to rest on, big tiles, concrete slabs, or whatever. Mine love places under shrubs and bushes where the dig shallow pits and lounge in there.
I wouldn't fix what isn't broken, if you are happy with his behaviour and such I wouldn't neuter. If you consider getting a second rabbit I would go for it though, intact males as house bunnies can be perfect, but with a second rabbit some issues arise, like seasonal humping and spraying. I have an intact buck and his spayed cuddlebun Dotty as free range house bunnies, sometimes there's some mopping up to do...
I started keeping house bunnies when my previous buck ventured into the house and behaved perfectly, after two years I got him Dotty, and things started to get a little more difficult.
Since he seems to be an outdoor bunny, I wouldn't worry.