Filler for plastic

[Debaser]

Hi folks, just putting together my first mod it's a front panel made from plastic, I'm not sure exactly what kind because it's a piece of scrap off the back of some appliance. Trying to fill in a few untidy joints. I've tried using Isopon, but it not really adhereing properly. Anybody have any ideas?

[nevermind1534]

Does it have to be clear, or can it be white or gray?

[Debaser]

It will be painted, so anything goes.