I don't know of any units that combine heating and dehumidification. However some dehumidifiers have very small heaters in them to aid in dehumidifying and to help deter frost buildup.
I've used several dehumidifiers over the years and the one I liked the best was a Soleus unit. It was very quiet and would work in lower temps than most but reliability was terrible. You're lucky to get a year or two out of them before the compressor fails. I've bought other ones since the two Soleus, but they're so noisy I'm still on a quest to find the right one. I'm currently using a Perfect Aire that I picked up from Ace hardware. It's just OK as it doesn't work in very low temps and is a bit noisy. I can keep it working in lower temps by putting a 200 watt heater directly in front of it.
Since you only have 30 amp service in your rig, you can only run one 1500 watt heater in your rig. You could potentially add another one if you want to bring in a separate extension cord from the site power post.
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