What Matt said.
Just beware of one twist - In a few battery "Groups" the Terminals can be switched, where the "+" and "-" terminals of the Replacement are on opposite ends from the Original. Probably not in Group 78.
We don't have a Costco membership but we do have Sam's Club. Batteries are one of those things you seem to have to shop every time you need one. We were getting vehicle batteries along with RV "House" batteries at Sam's. This last time it turned out WalMart was the better deal, at least for Chassis batteries. Then we needed a House battery right at the start of a trip and it came out WM again. Sometimes one from an "auto parts store" worked out better but not so much lately. Prices centered on $100, no-cost exchange, 3-yr on Chassis and 1-yr on House.
EDIT - The "Groups" are set by a council called BCI (Battery Council International) and this is their
BCI Group Chart. The GP78 has only one terminal layout. It was the GP24 and GP27 that I remember getting jammed up on.
