Steve here is my 2 cents. If you know for sure you can't take your amp on a tour or a fly out gig, contact the talent buyer or the sound guy and let them know your stage plot and that you need a small bass amp. Most professional sound guys or companies will already have some kind of back line bass amp on stage. If you can't bring your pedal board with your Pre-amp(s) and tuner just pack one in your case. Since my pedal board is in a hard case it's worth me spending the extra $25 baggage fee on a flight to bring it with me.
You can even get a road case for your small G&K amp and fly with it. I bring my G&K mb150 everywhere I go, and will use it on stage even if they have another bass amp already set up. I've have learnt my lesson time and time again....so I just cut the sound guy out of the equation as far as stage volume/monitor. One time at a nice theatre up in the Bay Area, during load in / sound check the sound guy saw my small G&K, gave me a nasty look and said "oh you won't be needing that, don't use it". I followed his advice thinking he knew the rooms acoustics. Of course during the performance the sound changed, I couldn't hear myself, I asked twice for more bass in the monitor, didn't hear any difference and the whole time I was playing I was regretting listening to him. That was my last straw and learnt my lesson.
My GK gets my pickup, then I send the house two signals: My DPA mic and my pickup and let him blend the signals as he pleases. I hate having to 100% rely on unknown sound guys who A.) potentially don't know what they're doing, B.) have crappy monitors, C.) have to much stuff going on and can't spend tons of time raising/lowering my bass volume and EQ'ing to how I need it since you have like 10 minutes to sound check the whole band at a festival D.) are potentially abrasive towards musicians for whatever reason.
When you tour and play festivals you never know what you're walking into and have to assume the worst. If the worst happens, you know 100% that you're going to be at least happy with your on stage volume and EQ since you have your amp and pre-amps that you know how to use and YOU have full control over it. My advice is to bring your pre-amps and a small combo amp everywhere you go as possible.
