vinyl joints for MDF paneling

[MoGamma993]

I'm putting MDF paneling in my bathroom, but for some reason, am having real problems getting the panels to fit into the vinyl joints and corners. I understand that it should be a snug fit, but I can't get the paneling to fit in any of the joints at all--instead, it just starts to peel away over the top of the joint. I've thought of thinning the backside of the panel, but wanted to see if anyone here could suggest some clever trick first . . .
Thanks in advance for any help!

[Sawdustguy]

From the backside of ot the panel, take either a belt sander or a piece of belt sand paper wrapped around a block of wood tightly and bevel the backside at least 1" with a taper.

[Sawdustguy]

Mogamma? How did your project work out?