You gave few details go on. A Google search for "Travel master Pompano" only shows 1986 on NADA Guides. It doesn't tell on what chassis it's built, since you did mention Chevy 454 I'm guessing Chevy but you don't tell if it's a P30, P32, P34, or something else. NADA doesn't list capacities but says the RV might have an auxiliary fuel tank.
If you crawl underneath you can take rough measurements of the fuel tank and get an idea, or just drain what's in it and then fill it up.