salaams brother...
No need of any letter...i have a car with bank backing but i just drove thru...also no need of letter from comapny either...
mind u it depends in ur company regualtion too..if not no issue whats so ever..
dont forget to get an insurance cover at the saudi border...its abt Qr100 depnding on the number of days...

Tc and ask dua for all muslims...
May Allah accept ur umra
salaams