RV Wholesalers and PPL motorhomes both have good parts departments. Of course amazon can be your friend as well.
Before you buy parts, tell us the year and model of the pop-up. Also, what is going on with the furnace that makes you think you need a control board? What kind of faucet do you have in the camper (hand pump, or does it look like a residential faucet)?
Current TV:'14 F350 Lariat CrewCab, 4x4 Short Bed SRW Diesel w/ Pullrite 2700 (16K)
Current Fiver: '15 Puma 295BHSS Anniversary Edition
Past TV: '13 F150 HD Payload SCrew EB, '08 Tundra CrewMax 5.7L, '02 'Burb 5.3L, '97 Dakota 3.9L
Past Trailers: '09 Wildwood LE 27RB, '02 Palomino Yearling RL, '87 Jayco 1006dlx