\documentclass[portrait,fontscale=1,margin=0.2cm,paperwidth=15truecm, paperheight=1.5cm,debug]{baposter}


\begin{document}

\begin{poster}{
  headerheight=0pt,
  columns=3,
  background=none,
%   linewidth=0.5pt,
  borderColor=red,
  textborder=rectangle,
  headershade=plain,
  headerColorOne=green!60,
  headershape=smallrounded,
%   boxheaderheight=1.5em,
  headerfont={},
  boxColorOne=lightgray,
}{}{b}{}{d}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{posterbox}[column=0,boxColorOne=lightgray,height=bottom,headerborder=none]{none}
\end{posterbox}

\begin{posterbox}[column=1,boxColorOne=lightgray,height=bottom,headerborder=open]{open}
\end{posterbox}

\begin{posterbox}[column=2,boxColorOne=lightgray,height=bottom,headerborder=closed]{closed}
\end{posterbox}

\end{poster}

\end{document}