J.P.
To make changing the sheets easier, try this:
Put on the fitted sheet.
Put a disposable, waterproof "underpad" on the section he's most likely to leak around.
Fold a top sheet in half and put over the underpad, tucking in the ends.
Finish making bed w/ regular top sheet, blanket, etc.
When a leak happens in the middle of the night, you just have to remove the folded sheet and underpad and (hopefully) it will be dry underneath.
Sometimes I even uses 2 layers of underpad and sheet...just in case there's more than one accident.
You'll still have to do laundry, but at least you don't have to make the bed in the middle of the night.
I agree w/ other posters who suggest larger and overnight diapers to prevent the leaks.
Good luck,
J.