Using primer on the trees

Hey guys, this may seem like a silly question, but I always get good responses on here.  

I'm working on a low rider model and I am doing most of the interior and engine in gloss purple and candy magenta.  I'm noticing as I paint the parts on the tree that it is taking several coats of paint to get good coverage and even then it still looks spotty in some places.  I'm still too new to the model car hobby to want to use an air brush.  I am using primer for the body parts and I am considering using primer on the tree parts as well.  Is that something most of you do or is just using multiple coats the way to go to get an even looking paint job.

 

Thanks in advance for the tips and opinions.

Source: http://cs.scaleautomag.com/SCACS/forums/thread/1021013.aspx

Marcel Balsa Lorenzo Bandini Henry Banks Fabrizio Barbazza