Hi Martin,
I use 3mm plastic 90 degree angle and mitre it. Realy easy to cut and stick with either cayno or plastic weld.
As you can see I have used differnt sizes throught the boat.
Hull is made from 5mm ply the bottom is made from 2mm ply due to having to bend it as there are a number of compound curves underneath , then glassed.
Superstructure is from 3mm plastic all other bits and fittings are either 2mm or 1mm plastic card.
Regards
Colin