Just happened to be looking on here...
How you should trimp depends on how steep the surface is. I'll sort them into three types of surfaces. You have gentle slopes, steep slopes and basically-a-wall slopes.
The easiest kind of trimps involve steep slopes. Steep slopes are the kind like on Degroot Keep where you just charge into the ramp/rock and you fly off it, no spacebar required for this one. All that matters is finding the right angle. You can find these by experimenting with the map terrain. Binding a key to impulse 101 and enabling sv_cheats 1 will help you experiment offline.
Second easiest are the basically-a-wall slopes. These are slopes that are so steep that you can't walk up them, and you also cannot charge directly into it, but they're not complete walls, meaning you can charge up them with a jump. All you need to do for these is stand directly next to them (to the point where you're touching them!), then jump and charge at the exact same time. That's it. You are now a climber.
Lastly we have pretty much everything else. Gentle slopes. Hills. Stairs (if they're clipped). Ramps that don't normally launch you. Even control points can work. For these you need speed. The more gentle the slope, the more speed you need. The only thing that's required is you be airborne, and hit this slope or ramp at a significant enough speed. Assuming you do that, you will fly.
The best way to gain speed is to do chargeturns whilst mid-air. A.K.A. Charge strafing. Charge strafing is basically W strafing on steroids. In short, ignore the A and D keys because they do nothing while charging. Just use your mouse to strafe, and try to look 90 degrees to the left or right of your current trajectory whilst strafing. This acts as a "replacement" for the A and D presses you would normally do in an air strafe.