I did last summer
I have a 32 ODay and I removed my stove and cut the plywood on one side facing the ice box and was able to slip another 1" piece of insulation on either side next to the 1/2" that ODay installed, on the opposite side which face's the enging room I put a 4" piece of insulation and was able to get some liquid foam into the cavity behide the plywood so that side has the original 1/2" plus 4" and what ever liquid I got in there. The side that faces the oven got about 3" and I noticed a huge improvment this summer and I'm ready to convert the box to a reefer unit.Before doing this I looked over the whole ice box installation and saw that there were voids,then I drilled inspection holes to see how to approach the operation,I helped a friend do the same with his Catalina using the same method.