This is a generic pic of what I think you are dealing with. One end has the bolt the other swings as I recall. All lines, wires and fuel neck off first if possible or as tank comes free (can be stuck on top also) have support while you deal with connections.
They use like roofing material which gets pretty sticky sometimes and may have that on top of tank as well. The idea is no metal to metal contact which in use could rub a hole in the tank or make a spark as no matter how tight you make a vehicle things need some allowance to move with the conditions we put them under.
The strap will pull off or call it peel off such that tank can be removed. If that insulating stuff is not up for reassemble ask your parts store or literally check out hardware store type product to replace it. Not sure you can buy what they call "ice shield" used here for roofing under shingles in small quantities but a tape or something should be available if it needs refreshing.
Universal replacement straps should be an in stock item - depending on where you are. Here rust would look like in pic above as early as a five year old vehicle and of course you can't safely use heat to help. I've just taken tin snips to straps and either welded back or put a piece over cut with rivets to make it reusable in not cut in a spot as to rub on the tank.
First get it out. If you are uncertain as to how to safely remove the pump + gauge sender assy hit back. REMEMBER - AN EMPTY TANK STILL HAS FUMES FAR MORE APT TO EXPLODE THAN FULL ONE WHICH IS TOO HEAVY TO DEAL WITH AND WOULD SPILL OUT WHERE FILLER NECT WAS SO IT MUST BE EMPTY OR VERY LOW.
More: If the tank is severely rusted you may be surprised that for a common Chev truck they probably are NOT all that expensive aftermarket but made to fit right new one. Use wood between any jack or jack stand used for support between metal of those and the tank. Do keep a fire extinguisher right nearby and having a helper is really handy for a couple critical moments while doing this stuff.
Good luck,
T
_________________________________________
Tom Greenleaf - MetroWest, Boston