Wouldn't this work? No fumes, water based, and inexpensive. Unless there would be some adhesion problem with the old paint on the cab.
" waterbased non-toxic wood filler is the most versatile we've ever used. Straight from the jar it works easily for filling nail holes, dents, and cracks in furniture or flooring. It dries in as little as 15 minutes, exhibits almost no shrinkage, and sets up hard enough to handle machining and fastening just like the wood around it. Slightly thinned with water to the consistency of ketchup, Famowood becomes a superb surface filler, leveling pores and hiding texture very smoothly. It sands beautifully, without loading your paper whether hand or machine sanding. It is fullly compatible with most water- or solvent-based stains & finishes. Famowood is non-combustible & virtually odorless. Colors can be intermixed to create custom shades, & can be further modified with UTCs."image (resized).jpeg