DSF

is it possible to sublimate onto fibreglass?

I would guess that it would struggle to take the required heat/time. Only one way to find out I guess. You might be able to get certain fibreglass for higher temps like they do for the car industry etc as I would guess there are different specs. I tried various frp materials in the past as it's a standard material for subli but not all withstand heat.

Many moons ago I used to work at a GRP company and did dry to sub onto a gel coated piece of GRP, it worked ok, the image came out fine. Just my two penneth