“3 gallons of each product”
(POR and House paint)?
I'd get 3 gallons of each product. If you can buy them locally, you can return unopened can/cans.
You should be able to get the house paint "pre-mixed" (off-the shelf).
An unopened can should be accepted as a return?
Can you find the POR locally - if yes, an unopened can shold be accepted on a return.
I have only done this on a 19' flat bed truck.