how to add seconds to a TimestampTz

Is there a better way than going to time_t and back?  I am currently
using this:
db->next_worker =    time_t_to_timestamptz(timestamptz_to_time_t(current_time) +                  autovacuum_naptime);

(db->next_worker is a TimestampTz, as is current_time.
autovacuum_naptime is integer for a number of seconds)

but it doesn't seem clean, and the comments in the functions more or
less say that their use is discouraged.

I saw about doing it via the interval input/output but that's an awful
lot of work ...

Is this the first time this is going to be done in the backend?

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support