It is 'easier' to get financing through the dealer, but you may pay through the nose in money and/or trouble. There are a number of common tricks dealers use and a few down right scams by some.
Before you go shopping for a motorhome, have some external financing lined up. That way, you can compare to see if what the dealer is offering you is in line or outrageous. Also, you can generally dicker either on the price or the financing, but often not both, so having your own financing may get you a better deal.
I didn't do my homework, so ended up with a finance package which was for 20 years instead of the more usual 10 or 15 years, and at a rate about 1/2 a percent higher than a quote I got (later, darn it) from an internet based RV financing specialty firm.
By the way, don't forget not to give out your social security number to anyone until you have already pretty much decided to do business with them. Many will say you 'have to' but cave when you tell them they have no legal right to it and will report them for SSN abuse if they persist in demanding it.
Insurance companies are notorius for using credit reports in making offers. I refused to give my SSN to any of them, and most responded with a quote after I said 'it must not be too bad, cause they just gave me a $xxx,000 loan'.
Don't give your SSN to the dealer until you have agreed on a financing package subject to a credit check. Some dealers will send it to many institutions, who each do a check. If you don't then take one of those offers, it is likely that your credit will suffer from lots of inquiries with no resulting loan.
If any company won't give you any information without a SSN, don't deal with them.
John (40' 2004 Country Coach Inspire DP)