The 'Call Size' (the size you ask for) on 'ALL Manufactured Housing doors & windows' is the Rough Opening or the 'framed opening'
(2x4 to 2x4 , Floor or jamb to the header) in the house.
Standing Outside and looking at the door if the hinges are on the left it is a Left Hinge else it's a Right Hinge
All measurements are in inches.
There are 3 main types of Storm Doors. Three Hinge, Four Hinge, And Residential Flush-Mount
Standard 3 or 4 Hinge Residential Flush-Mount Standard measured widths for 3 & 4 Hinge Storm Doors are: 32 34 35-1/2 36 38
Standard measured heights are: 71-1/2 75-1/2 77-1/2 79-1/2 81-1/2
The Call Size for a 3 or 4 Hinge Storm Door is the measured width + 2 and the measured height + 1/2
So, a door that measures 32x75-1/2 with 4 hinges on the right (outside) would be a Call Size 34x76 Right 4 Hinge
Standard measured widths for Residential Flush-Mount are: 31-1/4 35-1/4
Standard measured heights for Residential Flush-Mount are: 74-1/4 78-1/4 80-1/4
If your measured width & height both closely match those above your door is a Residential Flush-Mount
For the Call Size add 2-3/4in. to the width and 1-3/4in. to the height
So, a door that measures 35-1/4 x 78-1/4 with the hinges on the left (outside) would be a Call Size 38x80 Left Hinge Residential
If your door does not match these measurements to within 1/8 in. it is most likely not a Mobile Home Combo Door.