Hey Steve-O,
It should be doable with these long summer days. Obviously bring a headlamp or two to be sure. To do all three it would be best to make a loop starting from Diamond Notch @ the end of Spruceton Rd. (County Route 6) which is off of RT 42. SWH is the toughest of the three, so you may want to get it out of the way. Take the Diamond Notch Trail to the Devil's Path and go east towards Devil's Acre lean-to. There's a herd path (not far from the lean-to)along an old railroad bed which leads to the summit of SWH, but be prepared to use map and compass regardless. That area is also notorious for some pretty thick spruce. Long pants/sleeves may be in order.
After this, just take the DP the rest of the way to the yellow Hunter Mt. Trail, head on up and enjoy the view from the tower. Then go back down the Spruceton Trail (jeep road/horse trail) about a half-mile, 'whack up on the ridge and travel west to Rusk. From Rusk, you can 'whack back to where you started.
Alternatives: Do the loop in reverse, w/ Rusk first.There's a sharp switchback near Hunter Brook. This is a good place to take a bearing for the ridge that holds up Rusk. After finding the canister and signing in, then you could walk that ridge east back towards Hunter.
Or... if you do SWH Hunter first, you could also 'whack up from Diamond Notch near the bridge that crosses the West Kill. It's more hardwoods on that side, so you'd avoid the thickest spruce. It is pretty steep terrain though and you'd still have to come out the other side to continue to the main summit.
As for car camping, Devil's Tombstone is on the other side of Hunter in Stony Clove, and there's others that aren't too far. Here's a link:
http://www.dec.state.ny.us/website/do/camping/catskills.html
How this helps. Enjoy and be safe.
Matt
PS- Oh, and I almost forgot-don't forget to check out the viewpoint below the main summit of Hunter. It's not a panorama, but many folks like it even better than the view from the tower. There's a little spur to the west where the Becker Hollow Trail meets the yellow Hunter Mt. Trail.