Some new gaskets come with plastic tabs. If so stop tightening when you see plastic tab start to compress. And for a foam rubber gasket, RV places get a lot for them. I think mine was $35.00
But first...take off inside cover, be careful not to break those air flap direction thingies and look with flashlight for where water might be coming inside and getting into roof system or leaking. Then tighten up bolts to same torque, then if still leaking tighten 1/8 of turn. Not a matter of how much you can torque but matter of getting water tight, so be somewhat gentle. When I did mine weight was a mystery to me also. See what model you have and then look on line for your model and see what shipping weight to see how heavy. I just rolled mine on its back and no problems, don't know if I was lucky or not as far breaking cover. But didn't want to lower down or lift back up. I also drew me up a little drawing so when I put elec back I could put it back where it came from.
After you get leak stopped, every year after that (usually pre-season inspection) give those bolts 1/8 turn to keep water tight. Then after many years when gasket no longer has a compressing room left, replace.
Hard to believe a piece of foam is only thing keeping water out. But it does.
