Hello
  We have a large double wide home that was built in 1997. Its a nice home as far as double wides go but the heating cooling system seems to, well, suck. The master suite doesnt get hardly any flow from the vents and we have to use supplemental heating and cooling. We are seriously thinking about installing mini split(s) to cool and heat the home and keep the original furnace as a backup.
  Anyhow i would like to hear some opinions on the feasibility of it from those here who have information on the subject. Also where would i go to figure out what size system(s) i would want? Thanks 

What kind of system is it? Have you checked to see if it and the ducts are in good working order? It is sort of sad to see a manufactured home with a poorly designed system when it is so easy to do once and then apply to so many units produced. Maybe something is clogging a duct. Maybe a duct has gotten disconnected. Are the filters and intakes clean? Maybe the fan is malfunctioning.
If you have a large open floor plan, it might work with one head for the main area, but the bedrooms are gonna be a problem. My guess is the windows and the insulation are 1997 code minimum so it might be difficult to get enough airflow to keep them warm or cool.

Pressure testing the ducts for leakage would be called when debugging flow on any ducted system if you can't fix it by other means. Sealing every seam & joint any accessible ductwork with duct mastic and using FSK tape to seal the seams of the air handlers will also improve flow. At the registers caulk or mastic seal between the duct boot and the finish wall/floor/ceiling too- 1001 tiny leaks add up to a big leak, and it all counts. Low flow due to blockage is possible, but a less likely scenario than leakage. As ICFHybrid points out, ducts can become disconnected with use, especially in systems where the ductwork crossing the separate sections of the manufactured home as part of the site-installation.

Any ductwork that's outside of the home's insulation layer needs to be insulated too. Many manufactured homes will have ducts under the floor that are more likely to be accessible/retrofittable than those where the ducts run above the ceiling.

Mini-split retrofits into manufactured homes that have electric hot-air or electric baseboard heating are somewhat common in the Pacific Northwest since there are substantial subsidies available.

Sizing the system always starts with a Manual-J type heat load calculation based on the R & U values, using realistic outside design temps for you location:

http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf

Most mini-splits don't have much heating capacity at temps below 0F- if "DENALI" means you're located in the AK interior it might only be a seasonal solution, but most coastal areas will be warm enough to get substantial heating season benefit out of them.