For doing smaller bodies as 1/25, you'd need to use what is called "surface tissue" cloth. I've used it in a few of my older castings and they too weren't horrendous. Even now in certain cases I still prefer the glass over polyurethane resin.
Yes 95% of the Jarmar ones were only garbage bin standard and most of the ones I've had of his did have the cloth in them, just never enough as a strong sparrow fart would blow a hole in them, but alot can be achieved in the smaller scales with fibreglass when you get "your way of doing it" worked out. The basics are all the same, but everyone has different techniques as most times what works for one doesn't always work for another..
It's your model and I'm gathering it's a fictious build in that it's not an exact replica of a 1:1 truck, so you build it the way you want and if the rivet counters don't like it, then they don't have to look at it or comment on it.