Normally a letter for staying in Company Guest House or accomadation requirement, goes along with booking for train or bus or any other mode of travelling facility. Company letter templates which has been developed for this purpose itself is suffice. Incase no such templates are available, a simple letter addressed to Admin Head or Travel Incharge (through the approval of your department incharge), stating the purpose of travel and number of stays required will do.
I hope you can draft it as per the need. Trust this clarifies.
Regards,