You have not had the opportunity to speak with a real estate agent yet so you are not aware of the exact value yet as nobody has shown you a CMA (comparative market analysis).

If I funnel the cashflow into my mortgage to pay down the principal, I will be reducing how much interest I pay on the mortgage over time (assume the mortgage interest is 4%), but I'm having trouble understanding if this is directly comparable (e.g. 4% mortgage interest vs 2-3% if I invest the money in bonds) since I'm not paying off the whole mortgage in those five years. 

Another important factor to consider is the cash you have available to work with or cash you have access to because the RV parks  and mobile home parks if done right are quiet cash intensive compared to rental property.

You could be cash flow positive and losing money.Simply comparing these two investments and not weighing them against others I would be inclined to take the 1800 for a class A location instead of 150/mo (maybe!)

I’ve checked out RE a bit in Moscow and you’re right...it’s nuts compared to lc valley. :) 

I'm thinking of 1031ing the rental as well, I've been comparing MF vs SFR, I've talked to few vendors.Last week I attend a seminar on new construction 4plex in UT/AZ, but found that CoC/cap rate is better with SFH.

If they find no leaks then definitely show tenants your prior bills to compare with the current one. 

@Thomas FryerA multifamily investment property would be a good way to earn additional rental income compared to a single family.

Underground storage tanks, chemical seepage into the ground, etc...

I guess I'm comparing it to other market driven rates like stock prices.