Which water heater to buy

Hello all! I am new to this forum and I am building a 26ft tiny. If someone with experience tell me which propane thankless water heater I should go with. It's gonna live inside my small attached utility room which I will have it vent directly outside right away, the little space won't be heated but that's where  I am gonna keep all my electrical/solar system on the upper half and all my water related parts on the bottom.  I just don't know if this will count as outdoors or indoors. It is located in Washington state near clea elum so winters can get very cold. Circled in the picture is where I am thinking of placing it and cutting out the vent.

Any info would be greatly appreciated.

Hi Aleksey;
I just updated my tankless heater.
I went with a Marey L-16 propane unit.
We love it, no electricity is required, works from #8 to #150 of water pressure, no pilot light, and a standard insulated  5" propane vent pipe.
Here is a link to my thread all about it.
http://permies.com/t/270210/propane-demand-hot-water-heaters