Also, I know that if I connected the two structures with a deck or carport, it could be considered an addition in some ways, would this be at all feasible using a mobile home as an "addition" to a traditionally built duplex by connecting them with a deck. 

When doing the comps you don't want to go overboard on the high end, but you don't want to go so far in trying not to stack the deck that you go to low and don't fairly represent your property.

For an extra 140 bucks a year I get an extra 1mil umbrella to account for tenants slipping down my steep driveway, deck collapsing etc.. .For the market rents.. there is a 64 unit complex that is booked solid at 1150-1350 a month across the street.

New roof: $5,000 New siding: $2,500 New drywall: $7,000 New plumbing: $2,000 New elec: $3,500 New flooring: $2,000 Painting: $800 Cabinets: $1,500 Fixtures: $2,000 Appliances: $3,000 Total: $29,300 Don't forget other possible expenditures...we have to do most of these things on most of our rehab houses:- HVAC (could easily run $3K)- Framing (if there is termite or structural damage)- Mold Remediation (could easily run $5-10K)- Doors (could easily run $1-2K)- Windows (could easily run $3-6K)- Bathroom vanities- Showers/Tubs- Subfloor/Trim- Main Plumbing Line Replacement- Outlets, Switches, Registers, Smoke Alarms, etc- Gutters- Soffit/Fascia- Garage Doors/Openers- Termite Treatments- Decks/Porches- Landscaping/Grading- Garage Doors- Chimney Repair/Chimney CapThat stuff could easily run another $30K...I live in a major metropolitan area (Atlanta), and generally spend about $30/sq ft for a lower-end gut rehab, and with typical houses around here of about 2000 sq ft, my typical gut rehab runs about $60K.So, if this house is in anything by a low-end neighborhood and in a typical location in terms of cost, $70-80K is probably pretty accurate for a ground-up rehab.

I converted the house from propane to natural gas, built a deck, replaced some fencing, and painted the outside.

The ones that can't will collapse like a deck of cards. 

Burnt through a bazillion saw blades in process, a lot more then planned, went through case after case of glue but holly-cow was it amazing looking when all was done. 

We also replaced the deck in the back.

One of the blades was missing a screw and its bracket was also missing a screw.Cost to fix all of these was $0.82

I have a 1st Mort on my PR, balance of about $97K, I also have a $50K Heloc with a Balance of $48K (served as a 2nd initially but has been used for a New Deck, Roof, Heat/Air Unit, etc over the years so I haven't hardly reduced the balance).