hi, i'll be happy to help you in anyway i can.
2005 sl500 is a pretty sophisticated beast electronically.
have you looked in the fuse box next to the light switch for a fuse chart?
the hardtop and the gas flap are not related so i would guess you have a couple of problems, they may or may not be fuse related.
have you recently had the vehicle jump started?
for starters, just so you know there is a cable for releasing the gas cap near the gas flap behind the inner trunk liner. so you dont run out of gas while were sorting this out.
i'm afraid theres really not much someone who doesnt know what he is doing and who has a mercedes dedicated scan tool at his disposal can do to help you.
do you have a reliable independent repair facility nearby?
contact your local mercedes benz club of america they can tell you who to avoid if nothing else.
p.s let me know if i can be of any further assistance.