What does it matter? You bought a RV with equity money. The RV depreciates just as fast with the loan on the house as it does with the loan on the RV.
There is no difference. Unless you're looking at just paying interest only which would be insane.
Especially given that HELOCs can adjust in rate, if you are writing off your HELOC interest you already have tons of debt so the RV loan would be written off as well and on top of that if you got into a pinch you can dump the depreciated asset which secures the loan and keep your house which is the better deal. Especially considering many states protect your primary residence so best to keep that debt free.
The entire premise is crazy for what amounts to a tiny savings on interest.
In addition, there is no reason to pay a higher rate on a loan with a shorter term. If you intend to pay off the loan there are no pre payment penalties (practically no bank has these in the States, Canada is different) so make the lower payment or make a larger one if you want to pay it off faster. There isn't a benefit to paying 1% more for a shorter term when there is no penalty for paying it off early.
Banks love it when you pay them back early. They are lending at near historic lows with inflation starting to pick up. They love you paying them back early.
In addition, 725 is an OK score. Kind of middle of the road. You're at the bottom end of the good scores. Five years ago that would of been fine for the best deals now its kind of borderline. You need other tangibles like down payment and income from most banks.
http://www.creditscoring.com/creditscore/distribution.html