(petitioner who was hired by county to manage county park lived out of petitioner’s mobile home on park property, even though not required to live in park as condition of employment; deductions associated with mobile home not deductible under I.R.C. Sec. 119 because contract for petitioner’s services did not require petitioner to live on premises; fuel expense petitioner incurred to operate park vehicles deductible because strict substantiation requirements inapplicable to “qualified non-personal use vehicles).