Not noticed this being a problem yet (yeah, we're from the lower climes, where bacon grease is a common food ingredient), but I did have a suggestion:
We regularly clean the kitty litter box. When it's dry from washing, we spray it thoroughly with Pledge furniture polish, let it dry, then add litter. Makes the shoveling so much easier...
That might work in an RV toilet, whether plastic or ceramic. And you don't have to put on gloves, reach in and rub it around. Just clean, let dry, spray, let dry, use it.
I will be keeping the Metamucil idea in mind, though, should it become an issue...
Now one more thing out there can help with the more aromatic part of doing one's bidnez: try this on the water's surface before sitting down:
Poo~Pourri