Cover letter for proposal

I had 4 total responses to my queries. Some asked for first 50 + proposal, separate bio. Should I keep the cover letter short? Something like...

Dear Mr. Agent,

Thank you for your positive response to my query. I have enclosed the first 50 pages of Sokorri's Operator for your review.

I would be happy to send you the completed manuscript,

Regards,

xxxxxx


What do you think?

I found the answer on another thread...please ignore this one.

Cheers,
Eussie