Delbert - I see two situations here: one is buying a product from a manufacturer in business and you assume they will remain in business; then they're gone like Travel Supreme, Western RV, National, etc. Second situation is you buy knowing you have an 'orphan.' I most certainly would consider buying an orphan if the deal was good enough (factoring in no house warranty) and if I was certain I could get the house and chassis serviced. Obviously most of the components (stoves, ACs, fridges, etc.) are off-the-shelf which present little to no service issues and may even be in-warranty by the manufacturer of the component. If I wanted an Alpine, I would need to be certain I could get the chassis serviced since Western RV (Alpine) produced their own chassis.
Best thing to do is to find other National owners and see how they are coping. I have driven a Trop-i-cal and thought it was a very nice unit for the money.
EDIT: Ned - we're thinking along the same lines here!