When your RV's washer P-trap dries out from non-use, gray tank odors will escape through the drain. Add water monthly, install a trap primer, or use a P-trap cap to maintain the water seal and prevent sewer gases.
An RV toilet that won't hold water usually has a faulty ball seal, blade seal, or toilet valve. Most issues can be fixed by cleaning or replacing the seal assembly, which typically costs $15-30 and takes about an hour.
Odor while traveling is pressure differential pushing tank air back into coach. Check vent for blockage. Add powered vent fan or 360 Siphon cap to solve. Also check Vacuflush ball seal for wear allowing odor bypass.