PacificaPaul, welcome to iRV2.com. We are glad to have you join us here. I would recommend that you have a qualified technician diagnose and repair the problem with the furnace. Mud dobber, wasps, and other pest could have built up homes that restrict the flow of air needed for smooth and proper ignition. Have it serviced and once you have it working properly you might want to concider installing screens over the vents at least when you are not using the furnace. Good luck and have a great summer!
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7