For Maggiore, try this: Camping Lido Cannero
Small and gets crowded but ace location and near an excellent public beach.
For Iseo, can thoroughly recommend this one: Camping Punta d’Orro Great waterside location with a decent bar on site.
For Garda, I can only give one I’d avoid near Torbole!
It’s crowded and a little less than enthusiastic on the service side. Camping Maroadi But anywhere up there is a fabulous location so try your luck elsewhere nearby.
For Como have yet to find a place I want to stay, so also interested in any recommendations.
As others say, the lakes will be busy beyond the very start of July, but wouldn’t let that put you off. At most campsites there are lots of German ‘regulars’ who delight in spending hours looking disapprovingly at non-regular guests from outside the Fatherland. I never get used to the prolonged stares. And they persist!
But it’s a wonderful part of the world and even when it’s busy the food, scenery and generally warm local welcome make it worthwhile.
If you’re hanging around for a week at a time, I’d probably head to Garda and Maggiore first as they are a bit more lively. But Iseo is gorgeous and some biking available too.