We are doing a loan using a Mobile Home (personal residence), an older vehicle and a new vehicle (purchased with the additioal proceeds. We currently have a loan with the Mobile Home, and and the older car, which purpose was to buy the Mobile Home. So the new loan would pay off the original and then additional monies would be given to purchase the new truck. Currently the rate and the fact that it is personal residence fall under HOEPA. Does the mixed collateral effect this in anyway? What about the purpose of the loan?

Mixed purpose won't matter unless it is more business than personal (then it wouldn't be subject to Reg Z). The purpose is critical. HOEPA does not apply to [§226.32(a)(2)]:
1. A residential mortgage transaction (construction loans, purchase loans, etc.).
2. A reverse mortgage transaction.
3. An open-end credit plan (HELOCs).

What you describe is a refinance with additional funds for home equity purposes, so HOEPA may apply.