  We present a compact, long-term nearly continuous operation of a
room-temperature Ca$^+$ optical clock setup towards a transportable clock,
achieving an overall systematic uncertainty of $4.8\times 10^{-18}$ and an
uptime rate of 97.8% over an 8-day period. The active liquid-cooling scheme is
adopted, combined with the precise temperature measurement with 13 temperature
sensors both inside and outside the vacuum chamber to ensure the accurate
evaluation of the thermal environment for the optical clock. The environmental
temperature uncertainty is evaluated as 293.31(0.4) K, corresponding to a
blackbody radiation (BBR) frequency shift uncertainty of $4.6\times 10^{-18}$,
which is reduced more than two times compared to our previous work. Through the
frequency comparison between the room temperature Ca$^+$ optical clock and a
cryogenic Ca$^+$ optical clock, the overall uncertainty of the clock comparison
is $7.5\times 10^{-18}$, including a statistic uncertainty of $4.9\times
10^{-18}$ and a systematic uncertainty of $5.7\times 10^{-18}$. This work
provides a set of feasible implementations for high-precision transportable ion
optical clocks.
