Ok - further legal info. I dug out my Business Law book. LOL - yes this one caught my attention. After research the name Big Horn is considered public domain and can not be copyrighted or patented. Now as for the last legal venue would be Trademarks. First trademarks must be renewed every 10 years, there are two types a state only or Federal. Both have 10 year limits in most cases. Now the next issue is it currently being used commercially by the original owner of the trademark - if not then even if they do have a current trademark registered, it is considered diluted under the Federal Dilution Act. Also I am not sure that you can trademark the word Big Horn - because of it is the name of a place and an animal) Example Big Horn Mountains as a place.
Now on to further research, I checked the federal trademark site for the word "big horn" or "bighorn" - and in fact the are a lot of registered trade marks using the word big horn - but they all have some style with it. That means that you have to include the actual drawing or symbol as well in this case - because the simple word big horn can not be trademarked. BTW I did not see any trademarks for rvs using the word. I did find for an example that DAIMLERCHRYSLER CORPORATION owned one for a pick-up, as well as , other companies for whisky, tires, ranches, muzzle loaded rifles, Golf apparel, hunting horns, casino services, binoculars, saddles, wheat flour, and Bentonite Clay. There were 58 records - many of them dead.
So it looks like even Heartland has not trademarked (at the federal level) the word and logo. Scott if you are reading this - for my wonderful service I will trade one upgrade - LOL...