@CA John posted:Hi TrainManMike,
Since you said you like to DIY, go to the Clever Models website.
They offer some outstanding paper models. Plus, they offer free samples that periodically change. As a freebie, they recently, posted a single tunnel portal that uses thin foamboard as the backing material. You could easily modify their design to make it fit your layout. I've purchased some of their models and I think they look great.
John
Thanks! I will check them out.