I suggest waiting for Lubuntu 18.10 if you are not ready to take some risks.

On the other hand I don't see why you wouldn't have a working LXQT session on top of Lubuntu. But I guess you need mote than the lxqt package.

I can describe my own experience: I have installed on top of Kubuntu 18.04.

That is what was reported in terminal:

sudo apt-get install lxqt The following additional packages will be installed: calibre calibre-bin desktop-file-utils featherpad ffmpegthumbnailer fonts-mathjax galternatives gconf2 gucharmap gvfs gvfs-backends gvfs-common gvfs-daemons gvfs-fuse gvfs-libs libbonobo2-0 libbonobo2-common libbonoboui2-0 libbonoboui2-common libdbusmenu-gtk4 libffmpegthumbnailer4v5 libfm-data libfm-extra4 libfm-gtk-data libfm-gtk4 libfm-modules libfm-qt-l10n libfm-qt3 libfm4 libgdata-common libgdata22 libgnome-2-0 libgnome-keyring-common libgnome-keyring0 libgnome2-common libgnomecanvas2-0 libgnomecanvas2-common libgnomeui-0 libgnomeui-common libgnomevfs2-0 libgnomevfs2-common libgoa-1.0-0b libgoa-1.0-common libgucharmap-2-90-7 libjavascriptcoregtk-4.0-18 libjpeg-turbo-progs libjs-coffeescript libjs-mathjax libjs-sphinxdoc liblxqt-globalkeys-ui0 liblxqt-globalkeys0 liblxqt-l10n liblxqt0 libmenu-cache-bin libmenu-cache3 libmuparser2v5 liboauth0 liborbit-2-0 libpodofo0.9.5 libqt5xdg3 libqt5xdgiconloader3 libqtermwidget5-0 libstatgrab10 libsysstat-qt5-0 libtidy5 libutf8proc2 libwebkit2gtk-4.0-37 libwnck-common libwnck22 libxfce4ui-1-0 libxfce4ui-common libxfce4util-bin libxfce4util-common libxfce4util7 libxfconf-0-2 libxres1 libyelp0 lximage-qt lximage-qt-l10n lxmenu-data lxqt-about lxqt-about-l10n lxqt-admin lxqt-admin-l10n lxqt-config lxqt-config-l10n lxqt-core lxqt-globalkeys lxqt-globalkeys-l10n lxqt-notificationd lxqt-notificationd-l10n lxqt-openssh-askpass lxqt-openssh-askpass-l10n lxqt-panel lxqt-panel-l10n lxqt-policykit lxqt-policykit-l10n lxqt-powermanagement lxqt-powermanagement-l10n lxqt-qtplugin lxqt-runner lxqt-runner-l10n lxqt-session lxqt-session-l10n lxqt-sudo lxqt-sudo-l10n lxqt-system-theme lxqt-themes pcmanfm-qt pcmanfm-qt-l10n python-apsw python-asn1crypto python-bs4 python-cffi-backend python-chardet python-cherrypy3 python-cryptography python-cssselect python-cssutils python-dateutil python-dnspython python-enum34 python-feedparser python-html5-parser python-html5lib python-idna python-ipaddress python-libxml2 python-lxml python-markdown python-mechanize python-msgpack python-netifaces python-olefile python-openssl python-pil python-pkg-resources python-pygments python-pyparsing python-pyqt5 python-pyqt5.qtsvg python-pyqt5.qtwebkit python-regex python-repoze.lru python-routes python-simplejson python-sip python-six python-utidylib python-webencodings python-webob python-yaml python3-xdg qlipper qpdfview qpdfview-djvu-plugin qpdfview-ps-plugin qpdfview-translations qps qt5-style-plugins qterminal qterminal-l10n qtermwidget5-data quassel quassel-data thunderbird xfconf xfwm4 xscreensaver xscreensaver-data yelp yelp-xsl Suggested packages: gconf-defaults-service samba-common libbonobo2-bin libfm-tools nautilus-actions desktop-base gnome-icon-theme libgnomevfs2-bin libgnomevfs2-extra gamin | fam gnome-mime-data coffeescript fonts-mathjax-extras fonts-stix libjs-mathjax-doc libwebkit2gtk-4.0-37-gtk2 devhelp compton compton-conf juffed lxappearance nomacs obconf-qt openbox qtpass screengrab | shutter vokoscreen zim faenza-icon-theme gnome-themes-standard cmst | network-manager-gnome cdtool python-apsw-doc python-cryptography-doc python-cryptography-vectors python-enum34-doc python-genshi python-lxml-dbg python-lxml-doc python-markdown-doc python-openssl-doc python-openssl-dbg python-pil-doc python-pil-dbg python-setuptools ttf-bitstream-vera python-pyparsing-doc python-pyqt5-dbg python-paste python-webob-doc thunderbird-gnome-support ttf-lyx xfce4 xfwm4-themes xfishtank xdaliclock xscreensaver-data-extra xscreensaver-gl xscreensaver-gl-extra fortune qcam | streamer gdm3 | kdm-gdmcompat Recommended packages: qtermwidget-l10n disk-manager perl5

Then (and some of those below may be what was lacking in your case; having Lubuntu, you surely don't need openbox; I leave it there because I'm just pasting here the data of my own experience):

sudo apt-get install openbox pcmanfm-qt lxqt-admin lxqt-common lxqt-config lxqt-globalkeys lxqt-notificationd lxqt-panel lxqt-policykit lxqt-powermanagement lxqt-qtplugin lxqt-runner lxqt-session lxqt-sudo nm-tray

Remember that I was on top of Kubuntu. When I selected the lxqt session, I was prompted to select a window manager, and I did select Kwin, which I prefer. Maybe you could select openbox, or you may install Kwin too.

Once in LXQT, I have selected nm-tray to start with the session under Session Settings.

Considering appearance, I would recommend the following:

Lxqt theme: Dark (I think it comes by default), there are others here but most look very bad.

Widget styles are the same as in Plasma/KDE. I'm not sure which ones come by default in Lxqt-only, because I have it on top of Plasma, but Kvantum can be installed from deb and the most common ones are present in the repositories; find them by searching "kde-style". More here.

LXQT has a nice launcher called runner.

More tweaks on Lxqt are mentioned in my other posts here and here.