What should I expect in terms of financing a used 5'er?

I just looked at Good Sams rates and am blown away by the high interest rates for purchases under $25,000!! Twice that of purchases over $25,000!!!

https://www.goodsamrvloans.com/rates/

Could be. Dealers can get you as much as 15 years or more. Not sure banks will let you have that length of term. Best to check around. Dealers will always work with you, but their interest is in their bottom line, not yours.

I would check your local credit union for financing. Also, I would read up on others who have purchased from Camping World.