I have tried a ramp in the past, I have only had the Saints that didn't need a ramp that would use one willingly!
A couple of mine will put their front feet in but I have to lift the back end in or they just stand there. Mind I do have a car at the moment rather than a van so it is higher for them to jump in than they would have to usually.
Think you've got problems now, wait til he's 80kg like my big girl, she's the worst for getting in!!