Easy; get some cheap silicon or ask every neighbour if they have any part tubes that they don't want and just fill narrow weak areas and corners of trays. This may make it heavy though. Another option is mix pl
aster Paris with p.v.a wood glue in a really stiff mix and fill. I've done this with...
Hi from Oamaru Sth island New Zealand.
For this it's amazing you will get a good set with other options from medium to budget brands like Fuller. I'm not sure if you have it it the U.S but they were in U.S around 1960', 70's and 80's.
I love the brand as it's pretty good and prices fair...