Is it permissible to pray by gesturing for bowing and prostrating while seated on a chair or car seat, due to the severe cold, the impurity of the place, and the difficulty of finding a clean place to pray?

If the guardhouse is dirty and there is no clean place to pray, that is not an excuse to abandon or delay prayer. A clean garment can be spread to pray upon.

If the place is impure (najis), and it is possible to purify a spot for prayer or to spread a thick, pure garment over the impure place and pray upon it, then that must be done. This is usually an easy matter.

If the worshipper is unable to do any of this, he should pray according to his ability, standing and gesturing for prostration. He should then repeat the prayer as a precaution when he is able to pray in a pure place.

Al-Nawawi stated in Al-Majmu': "This is our madhhab, and all scholars agree with it, except for Abu Hanifah, who said that one should not pray in it. Our evidence is the hadith of Abu Hurairah, that the Prophet (peace be upon him) said: 'And when I command you to do something, do of it as much as you are able.' (Narrated by Al-Bukhari and Muslim), by analogy with a sick person who is unable to perform some of the pillars." This repetition is obligatory according to the newer, more correct opinion, and recommended according to the older opinion.

The questioner must bring a pure mat to pray on in this place, and if that is not possible, he must seek another job that does not lead to neglecting prayer.