Forgive me, but I tend to sort of 'disagree' with the use of Future or any other varnishes as a 'barrier' between base camouflage colour(s) and washes (and even the final steps of drybrushing, 'dusting' and weathering)...
You pay a lot of money to get kits manufactured with recessed panel lines and super-details and then you give the model a multitude of coats (even if light ones!) that just tend to fill in panel lines and flood in details...
Most of my AFVs are normally painted with flat enamels. I normally use an airbrush for this as it allows for the best light overal 'coverage'. Next I'll paint on my markings (decals are just too thick) then use a wash made of watercolour (the artist's kind, in tubes), water, dish-washing detergent and vinegar. My usual mix at this stage is sepia and black. I might need one or two, sometimes three applications of the wash, depending on what I'm trying to acheive. Next is a thick wash of pure black that will go into grills, mesh, vision slits,... That will dry for a day or so, then I'll drybrush with artist oils (normally shades of yellows, greens, browns and/or white) then add stains and rusty spots: tiny dabs of burnt sienna on some rivet heads, bolts, hooks, and other locations. Use a clean dry flat brush to drag the fresh paint down. Do the same for oils/grease stains but with a darker colour (black + burnt sienna). Next with the airbrush and Humbrol's 29 Flat Earth colour (or sometimes just with a fan-shaped soft brush and pastel dust), I'll 'dust' the model. The oils used in the drybrushing part will make the flat base paint come alive, leave a certain shine that really looks good on AFV models.
For my aircraft, I normally use cans of automotive acrylic paint to do the base colours. I might use some enamels, either brushed on or airbrushed for anti-glare panels, ID markings and the like. Here, I'll use, after a couple of days after decalling, artist oils to do the wash. This is right before this stage that I might use varnishes or Future... But only to make sure the decals are protected and that the overal finish is uniform rather than having decals being WAY more glossy than the rest of the plane for instance. Anyway, back to the wash! Not slopping it all over like I would do on a tank, but I'll apply it directy onto the model with a fine brush. Turpentine or other white spirit alows me to thin the paint to the point where when applied into the recessed line, capillary action will take the paint all the way down the line. If not, I'll help along the way by nudging the paint once more along the recess. Any excess can be cleaned with a clean dry soft flat brush. Stains can be spread along the same way I'd do on an AFV model. Dark greys, brown and black in various mixes are what I use most on aircraft, but the shade you need depends on the colour you have on your model.
I think I get pretty good results with those techniques. It's fast which is good because I do not have much patience. And it saves messing about with gloss then flat varnishes (I've had my share of problems with yellowing varnishes and those that never seem to get flat enough...)