What are you guys using for extending the edges on a plug?
I have used card and foil tape but its too flimsy when you push a paddle roller over it for my liking.
Anyone using foamcard ? I suppose the foam would need taping over to prevet per attack
Typically I use playing cards. Apply a few light layers of mat after gelcoat to stiffen the structure up before hitting the area with rollers. Alternatively, for flat parts, I like foam boards (school project ones) covered in aluminum tape.
Thing is when I dad the bush on the mat the cards wobble and I have a couple of small cracks from doing that.
Thing is when I dab the brush on the mat the cards wobble and I end with a couple of small cracks. Its stiff where the cards lay flat but where they go diagonly across a lilte upstand (ot L shape) they flex a bit, perhaps I can stiffen it up with another layer of card.
EDIT: I agree 100% with what Perfeng said.
These flanges were made with posterboard with a hole cut in the middle and 3M aluminum tape.
I reinforced the posterboard/tape with small hobby aluminum tubes to prevent the board from curling when the gelcoat starts to dry. Worked perfect.
Hot glue paint sticks on the underside of the flange.
Yep using hot glue. Its not the attaching thats a problem just the wobbly card.
I use aluminum sheet (large rolls come in 24" x 20’(or so) and aluminum foil duct tape. Both available at Home Depot or similar
if its in an area that will possibly bend I’ll double up the aluminum.
I’ve actually been meaning to do up a DIY on flanges but haven’t finished on the rest of the pics. I’ll post up the basic on cutting the aluminum sheet tomorrow.
…or after an election, collect the election signs and do the local community a service! 
Thanks again guys!