Tires: RV tires, fifth wheel camper, rv tires

Question
I have a 32ft fifth-wheel camper/trailer with two axles.  Weight is probaly 9,500 lbs.  Tires are 15 inch (or 16??) trailer rated tire, 60psi max.  I have gone through two sets of tires, in less than 4500 miles.  They wear VERY unevenly, especially on the inner half, and more so on the rear axle.
Is this a tire issue, or a load/weight issue?  Or is the problem likely the axle and/or allignment of the wheel?
I know this is general info, if you need more specifics, I will try to provide.
Thanks

Answer
Chuck,

This is a vehicle issue.  Tires do not wear unevenly unless the alignment is off. So you need to check the alignment of the trailer.  

I'm not familiar with how this is actually done, but I know they have to reference the position of the axles relative to the fifth wheel.  But in particular, they need to look at camber - and possibly toe in.