Suburban furnace replacement for '66 Trade Wind

[Ben in MT]

Hi All! I have a 19966 Trade Wind with an original furnace (Suburban No. NT-20) that is obviously bad and as far I understand has been recalled. I'm trying to research what replacement furnace I should purchase to replace the OEM equipment and from what I can tell a similar furnace is still manufactured by Suburban referred to as a model number NT-20SE. The new model boosts 18,000 BTUs and as far as I can tell the old model produced 20,000 BTUs. My question is, will the loss of 2,000 BTUs be remarkable? I live in Montana and we want to stretch our season as far as possible, so to say the least I'm a little concerned with possible "under-heating" our 24' Airstream. Any consideration is greatly appreciated! Thank you in advance.