I agree with your concern about DEET and plastic and rubber degradation - so I try to minimize its use around those kinds of materials, and around cameras - sometimes I just use a tiny bit of high strength DEET ( 100%) across the back of my neck and ears and on my cotton hat, but not on a Gore Tex coat or hat. Not more than necessary, but enough for efffect. One can purchase 4 ounce plastic bottles of 100% DEET - that should last you for years of modest use. One other trick in heavy mosquito country that I think will work, but I have never seen suggested, is to wear the disposable blue vinyl examination gloves for ones hands - I doubt most mosquitos can penetrate that very effectively.
Usually, locally, I just use the Deep Woods OFF with 25% DEET and lightly spray my shoulders, neck, ears, hat and the backs of my hands if I am not wearing gloves.
The US military has treated its combat fatigues with Permathrin since 2003 - the permathrin is toxic if rubbed on the skin or inhaled, but once it has dried onto clothing it is no longer absorbable through the skin. One needs to spray the clothing until it is pretty damp and then let it dry, Do the spraying out of doors, do not inhale the fumes. I have done it several times out of doors - not an issue. Sawyer's says once spray treated, the effect should last through about 6 washings. The commercially treated clothing from Ex Officio and others, typically is said to last through 50 or more laundry cycles.
Make sure you spray your socks, bandanas, underwear, T-shirts, and a long sleeve cotton T shirt or sweater too. And your jeans if you are not wearing rain pants. Wearing Gaitors over your boots will help keep mosquitos off your ankles too. I like the Gaitors from Outdoor ReSearch that seal in the front with a full length Velcro strip - easy to put on, easy to take off, and keeps water, mud and bugs off your ankles, and will help keep ticks from climbing up your legs - I've never sprayed Permathrin on my Gaitors - but thinking about it, I might in the future.
DEET works better than permathrin for mosquitos in the Arctic (I believe), but permathrin immobilizes and kills ticks on contact, which is great! Particularly if you are not going to be bathing and changing clothes daily.
When I walk around a local lake in central Indiana I usually don't use anything, but when the humidity is very high for several days, and modestly cool, black midges or no see ums can drive you nuts trying to get into your eyes, ears, and noses - I think they're after moisture, they don't bite. DEET on my hat and maybe a bandana around my neck or suspended from my hat, drives the tiny black midges away and one can walk much more peacefully.
If I was only going to walk a 100 yards or so, I wouldn't do anything, but if one is walking for several hours, one needs a little peace and tranquility.
In Siberia, like Alaska, and Greenland, you will want all the tricks you can gather to deal with the mosquitos. You MAY, depending on season, breezes, temperatures etc, need head nets too. I used them in Greenland for photographing at sunset along the seashore. I have seen the sky turn black shortly after sunset in northern Canada near Hudson's Bay - without serious protection, you would be likely to die from blood loss...... modest exaggeration for humorous effect.....I think....