Schwintek slides have no problems as designed by Schwintek. It is the OEM RV builder that causes the problems. ALL the Schwintek system does is move the room IN and OUT. The room glides on floor rollers. If the Rectangle hole is not cut square, you will have problems
If the support structure of the wall cut out is NOT strong enough, you will have problems
If the slide room is not made square, you will have problems
If the OEM installers screw up on the install of the slide box, you will have problems that may not show up for a few months
Most Motorhomes that I have worked on that have Schwintek slides, the slides never cause or have a problem as a Motorhome wall is usually built strong with heavy aluminum or steel side structures on the wall outline. Towables have had numerous problems with all OEM's, because they cut down on reinforced wall studs to lower weight and some the flex of the frame will cause flexing of the slide hole cut out which will break components on the Schwintek mechanism. These type problem have almost been eliminated after a few years of finding the faults and beefing up the slide hole cutouts. I am not familiar with the Thor system but, a "double" rail does not seem correct. Like I stated, the room and weight is support by floor rollers (not part of the Scwhintek kit). With the Schwintek system loose from the RV, 1 person can push the room in and out on the rollers. There IS a weight limit for a Schwintek system and some OEM's go over that limit and try to modify the Schwintek to work and Schwintek looks the other way. Doug