The Last Dinosaur
Richard "Have Gun Will Travel" Boone hops into his drill car, drills under the Arctic, finds a lost valley of dinosaurs, and commences to shootin' because he's a MAN and MEN have to HUNT. A 1977 co-production by the people who brought us "Ultraman" and also the people who brought us "Santa Claus Is Coming To Town", this wild TV movie is jam packed with rubber suit monsters and sweaty sexism (Richard Boone's character is named "Maston Thrust") as everybody involved looks off-camera for that bottle of whiskey they stashed under a fake boulder, or a phone so they can call their agent and get themselves out of this mess.
A great suggestion! Boone's craggy face and booming voice as he constantly hollers at everyone is great stuff. Some okay suitmation bits and a fun bunch of subhumans to annoy our heroes adds to the fun. This would be a good choice.
Anything that has the macho hero yelling "YOU DING-D0NG!" in a towering rage is perfect Rifftrax fodder.
ETA: I didn't know "d-o-n-g" was on the list of Rifftrax's censored words.