Hi
@CamSincs. Take off one of the wheels and measure the distance in millimetres between two studs next to each other, centre to centre. You need to be pretty precise with that measurement. This measurement along with the amount of studs is the PCD. Holden and Ford have matching PCD pattern particularly in the common 114.3mm size. Once you have that PCD just Google it and you'll get the pattern. A Google search of "PCD 5x114.3" would give you both the common Ford and Holden pattern.
Equally important is to check tyre width and rim offset of the factory rims so ensure you leave yourself ample clearance, and the new rims and tyre don't impact of your brakes etc. Make sure the new size tyres don't impact on each other too. If you get any of that wrong it could result in a catastrophic failure.
You'll also need to check very carefully the overall clearances with the wheel and tyre within the wheel arch area along with potential wheel travel etc.
Cars have manufacture set specs on what size wheels and tyres can be fitted. It would be illegal and un-roadworthy to go outside that spec range. I can't give you any feedback for a caravan, but if was a car it would be very unlikely the spec range would allow you to go from 14s to 17s. To ensure your roadworthy, probably best check with Jayco themselves
