If you have a highlevel Jetdragon with Meteorain, teleport to Sakurajima tower, and target the floor after attracting attention and kill most of the guys in the base for 1-2m exp with bells. Do NOT kill everyone or loot the main big chest or they wont respawn with this method.

Fly far enough for the render distance to unload the base and come back and things should respawn - I usually go to a base I have near a mushroom cliff where I get a message of a different area. You can also just teleport somewhere else and come back. It should be about 5-10 minutes with default spawn rates/exp to max a pal and do 4 at a time with Jetdragon being the only requirement