Changing a flat tire is simple with the std leaf spring suspension if you have a shorty hyd bottle jack.
When I was on the road pulling work trailers I had a old Truckers Special 12 ton shorty hyd bottle jack made for lifting from under the axle tube as close as possible to the suspension U bolt. This jack comes with a short leg steel U channel that slips over the top of the jack and cradles the tube.
Eliminates the axle (s)from slipping off the small end of the jack.
Using this method just raises one end of the axle and not the side of the trailer. In fact the trailer won't raise at all.
As others say hooked to the truck or sitting on a pad some where doesn't make any difference.
Whatever method you use make a dry run at home especially if you go with a ramp type device. Some folks found out the hard way the ramp didn't raise the flat tire off the ground or not far enough to mount the fully inflated spare tire.
"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers
'03 2500 QC Dodge/Cummins HO 3.73 6 speed manual Jacobs Westach
'97 Park Avanue 28' 5er 11200 two slides