The classic method technical divers use to rig a stage or sidemount bottle is a compact or "brass & glass" gauge assembled with a very short high-pressure hose folded back on itself against the first stage and permanently tied in place with a piece of cave line. We do NOT recommend doing this with a rubber or flex hose because the hose is also permanently stressed at the two weakest points, the fitting swages. Although not as convenient to read, allow the SPG and hose assembly to lie straight against the tank while held against the side of the cylinder under a hose retainer. Because the short hose is less able to absorb the impact of rapid pressurization, we recommend following best practice to depress and hold the second stage purge while slowly opening the cylinder valve until the regulator begins equalizing with the cylinder pressure.
If you prefer folding the hose, then use a bungee loop (about 1 foot of 3/16" with the ends tied together in a fisherman's knot or we prefer an overhand loop w/pigtail) instead of cave line because when the regulator is off the stage the bungee loop allows the hose to be unfolded. Some divers also prefer using a slightly longer hose when folding, hopefully offering a reduction in stress on the folded hose. Regardless, in our experience all short rubber or flex hoses still may fail prematurely from being folded back on themselves. Recent availability of short high-pressure hoses with a braided stainless steel jacket, together with the bungee loop rigging method, seems to be the most durable and reliable compromise.
Here is one final thought... ask yourself "Do I really need a full size SPG?" Sometimes the exact amount of the gas remaining in an off-board bottle is not being used to control the dive. The only reason for the presence of the SPG on the travel or bailout bottle is the diver just needs an indication of cylinder contents as full, partial, or empty. If your diving application doesn't need an exact reading on gas remaining in the cylinder, an inexpensive button SPG will significantly reduce the number of failure points. This is especially true of bailout bottle applications, whereupon switch to bailout also terminates the dive and knowing the exact tank pressure is unlikely to be meaningful.